During gas shielded arc welding of steel railroad rails in the field, difficulties have arisen in the past when the welding of gaps were reliant on the operators ability to position the pieces of rail to within the specified weld gap limitations. As in the case of on-site welding of large essentially immovable objects, positioning pieces of welding equipment to within the weld gap limitations can be very difficult or impossible to accomplish. Typically, robotic gas shielded arc welding has been very effective when welding is performed under controlled conditions, such as in a test laboratory, and the item to be welded can be brought to the stationary robotic welder and positioned to produce a weld gap that is within tolerance. On-site welding of large essentially immovable objects utilizing gas shielded arc welding has been ineffective until this point because of (1) the difficulties in positioning an easily transportable robotic arc welding device precisely with respect to the gap between two pieces to be welded when the pieces are stationary and repositioning is virtually impossible, (2) positioning the pieces to be welded precisely with respect to each other to define the weld gap to be welded by a nominal weld program is difficult and (3) the inability to accurately cut the faces of the pieces to be welded so that the geometrical planes created by the faces, that define the gap, are parallel to each other.
It was desirable to design a system that can sense the location and size of the gap between two pieces to be welded and automatically orient the gas arc welder to the proper location with respect to the gap to perform the welding function. It was also desirable to instantaneously gather information during the welding process to adjust data to allow the weld program to adapt to the weld gap. It was desirable to store the weld program data in a format that allows for easy manipulation of this data during the welding process. When automation is added, it is possible to properly align and modify the weld coordinates so a sound and accurate weld can be produced between two pieces.